As a great agricultural country, China continuously increases the yield of crops with the development and popularization of the agriculture science and technology. Since the mulching film functions for heat preservation, moisturizing, promoting the growth and development of the crops and increasing the yield, the application of the mulching film as a modern agricultural technology has had a large effect on increasing the yield of the crops, increasing the income of farmers and promoting the development of the agricultural production. However, due to the widespread use of low cost plastic film, and the plastic film is not degradable, bringing the “white pollution” and the soil compaction, permeability deterioration, decreased soil strength and other issues. Therefore, various mulching films which are partially or completely degradable are developed on the market, such as starch-added bio-degradable agricultural mulching film, photodegradable agricultural mulching film, plant fiber mulching film or the like. However, in the currently developed starch-added degradable mulching film, the mass fraction of starch is only about 20% to 30% and only the starch in the starch-added degradable mulching film are degradable, while a majority residues of polyolefin film still exist in porous structure. Thus, the problems of “soil hardening and reduced soil fertility” in the farmland cannot be completely eliminated. The plant fiber mulching film is mainly a paper mulching film. The paper mulching film is completely degradable in the soil, pollution-free and environment-friendly. However, the paper mulching film is low in strength, poor resistance to wind and rain, easy to be damaged, easy to be broken when in laying and unsuitable for mechanical laying. Therefore, in the actual use, the film laying is difficult, time-consuming, labor-consuming and higher in cost. Patent (CN 201010262355.x) entitled “plant fiber non-woven fabric and production method thereof” discloses a bast fiber mulching film and a production method thereof. The method is carding bast fibers through a carding machine to form an initial net and then forming a finial net through an air-laid machine. The bast fiber net immersed in a chemical binder and chemically bonded; a fluorine-containing water repellent is used to perform waterproof treatment; and the net is dried and consolidated at one time to form the film, and finally the film is calendered through a cold calendar and coiled. Since the net forming speed of the air-laid machine is as low as 20 to 25 m/min only, the production efficiency is influenced and the cost is increased in the mass production process. Meanwhile, the chemical binder PVA is incompletely degradable and is gradually deposited in the soil after long-time and repeated use, which may severely damage the soil. By adopting an immersion binding process, the water content of the bast fiber net is high in the immersion process. More energy is consumed during the drying and consolidation process, and the production efficiency and the production cost are severely influenced. Therefore, the disclosed process is complex, excessive procedures are needed, the equipment investment is high (numerous equipment), and the production cost is high. Meanwhile, the bast fiber mulching film cannot be completely degraded and cannot be free of pollution.